This invention relates to imaging members and to methods of providing imaging member substrates with nonreflective surfaces.
Embodiments of imaging member substrates to be used in xerographic printers employing laser light should have a non-reflective surface. If the surface is reflective, the resulting printed copy will have an undesirable defect referred to as "plywood". Plywood is a print quality defect that results from non-uniform discharge of an imaging member. The defect consists of a series of dark and light interference fringes which occur when a multilayered imaging member is used under a coherent illumination source, e.g., a laser beam. The interference fringes are caused by the reflection of the incident beam of coherent light from the imaging member's interfaces. Specifically, the reflections from the top surface and from the metal ground plane (the substrate) cause most of the interference. The interference can be avoided by eliminating or suppressing the strong substrate reflection. This is generally accomplished by roughening the surface of the substrate.
Methods of rendering imaging member substrates non-reflective include, for example, anodizing the substrate surface, dry blasting, adding scattering materials, coating the substrate with an opaque and nonreflective layer, critical machining which uses special diamond cutting tool designs, and roughening the substrate surface by honing techniques, e.g., wet honing by means of glass or ceramic beads or spray honing wherein the substrate surface is sprayed with particulates in water media.
Each of the foregoing methods requires the additional step of subsequent washing of the substrate. Coating the substrate with an opaque and non-reflective layer requires not only a subsequent washing step but also additional materials, i.e., the materials used in the opaque and non-reflective layer, and the additional step of applying the layer and curing it. Critical machining processes using special diamond cutting tool designs are demanding and have tight process latitudes, resulting in diamond wearout and usage with lower yields and throughput. Honing media are expensive, which leads to high processing costs. Spray honing is also a source of contamination defects on the substrate. Furthermore, startup and shutdown of the spray apparatus causes spray material to dry on the nozzle, which contributes to process and defect problems. Spray honing also involves waste containment costs and a risk of environmental pollution.
Methods for rendering imaging member substrates non-reflective must not only eliminate or suppress strong substrate reflection, but they must do so without affecting the electrical parameters or the print quality of the imaging member. Furthermore, the method should render the substrate surface clean and give it uniform roughness and allow the substrate to remain hydrophobic.